A stroke is largely divided into two types of strokes. One is an ischemic stroke caused by an ischemic state of a brain tissue because of reduction or blocking of blood supply to the brain tissue, and the other is a hemorrhagic stroke causing bleeding in a brain tissue by rupture of a blood vessel. Since about 80% of all stroke patients have the ischemic stroke, and about one third of ischemic stroke patients undergo death, the ischemic stroke can be said to be a serious disease. Especially, the ischemic stroke is caused from insufficient cerebral circulation of blood, which is caused by the blocking of inflow of arterial blood. In general, appropriate supply of brain blood is secured by an arterial system within a brain. However, various diseases, including an inflammation, and atherosclerosis, may cause a thrombus, that is, a blood clot generated in a blood vessel. The thrombus may obstruct an arterial blood flow, thereby causing cerebral ischemia and its accompanying neurological conditions. In addition, the ischemic stroke may be caused when an embolus, that is, a piece of thrombus formed from a heart, blocks a blood vessel. It causes a decreased pressure of perfusion or an increased viscosity of blood as well as an inappropriate flow of brain blood.
There are two treatment methods capable of being used for the stroke. One method is to reduce a lack of oxygen and glucose in an artery by increasing a blood flow, and the other method is to protect a neuron by blocking nerve destruction induced by cerebral ischemia and excitotoxicity. Clinically used neuron protective agents include a calcium channel blocker, an MNDA receptor antagonist (a kind of glutamate receptor), and the like. However the treatment methods show a low effect while having a high incidence of side effects. Accordingly, it is urgently required to develop a method for increasing the effect of the treatment agent and significantly reducing side effects on a normal tissue.
Meanwhile, the method for diagnosing the stroke as described above is divided into a preventive diagnosis method, and an onset diagnosis method. The preventive diagnosis method representatively includes a blood test, and the onset diagnosis method includes a blood test, a transcranial Doppler method, a computed tomography method, a brain magnetic resonance imaging method, a cerebral angiography method, and the like. For the conventional preventive diagnosis method of a stroke, there is no authorized reliable blood test so far. For the onset diagnosis method, although various methods have been developed and clinically used, most of them can only determine an injured region, but there exists no diagnosis method for determining if the injured region is a penumbra capable of being recovered again and for predicting the prognosis of stroke treatment. Thus, there is a limitation in determining a treatment course.
Meanwhile, a drug delivery system or a target therapy which is for selectively delivering a drug to a specific tissue has been a highly interesting technology. This is because even though a therapeutic agent is used in the same amount, it is possible to increase the effect of the drug, and at the same time to highly reduce the side effects on a normal tissue. In addition, when the system or therapy is applied to a gene therapy, it is possible to increase the therapy efficiency and to reduce serious side effects by selectively delivering a virus to a specific tissue. For this, an antigen specific to a specific tissue, and an antibody targeting such an antigen have been mainly developed so far. However, in a case of an antibody, there is a problem such as an anxiety about an immune response, a low efficiency in tissue penetration, and the like. On the other hand, a peptide is advantageous in that due to its low molecular weight, an anxiety about an immune response is low, and its penetration into a tissue is easy. Accordingly, when a target peptide is connected with a conventional therapeutic agent, it can be utilized as an intellectual drug delivery carrier for selectively delivering a drug to a specific tissue. Thus, it is required to develop a target peptide.